The present invention relates in general to an apparatus for chemical-mechanical polishing (CMP) of semiconductor substrates for polishing and flattening a surface of the semiconductor substrate. More particularly, the invention relates to a semiconductor substrate holder for holding the semiconductor substrate to be polished whereby the substrate is held and pressed against a polishing pad. The holder contains a main body for holding the semiconductor substrate in a predetermined position relative to the main body. The main body has a base plate and a ring-shaped elevation provided thereon. A pressurizing device is provided for pressurizing the semiconductor substrate from inside the ring-shaped elevation towards the underlying polishing pad.
In the processing of integrated semiconductor wafers and integrated circuits many process steps require a subsequent flattening or planarizing of the semiconductor topographical structure. Therefore it is highly important to provide a method and an apparatus for polishing and flattening the surface of the semiconductor substrate to a high flatness degree.
In order to achieve the extent of planarity and thickness homogeneity necessary to produce ultra high-density integrated circuits, chemical-mechanical planarization processes are employed. The chemical-mechanical planarization or polishing (CMP) processes involve in general pressing a semiconductor wafer against a moving polishing surface that contains an abrasive material or is wetted with a chemically reactive, abrasive slurry. The slurries are either basic or acidic and may contain alumina, silica or other abrasive particles. Typically, the polishing surface is a planar pad made of a soft, porous material, such as polyurethane foam or non-woven fabric, and the pad is generally mounted on a planar platen.
A major obstacle for the achievement of a high planarity and a high thickness homogeneity of the surface of a layer to be polished lies in the fact that either the semiconductor substrate below the layer to be polished or the polishing pad may contain thickness or surface variations due to warping or waviness of the wafer or the polishing pad. These variations would normally lead to corresponding local variations in the pressure applied to the semiconductor substrate during polishing and thus to local variations of polishing rates. The construction of a semiconductor substrate holder should therefore provide facilities that would allow to compensate for the inhomogeneities.
A simple configuration of the substrate holder includes a rigid metal plate for pressing the semiconductor substrate against the polishing pad. The standard construction, however, does not allow for any compensation measures for inhomogeneities of substrate thickness or polishing pad thickness.
In U.S. Pat. No. 6,012,964 a semiconductor substrate holder (carrier) is described which is constituted by a housing, a carrier base, a retainer ring, a sheet supporter, a hard sheet and a soft backing sheet. The sheet supporter is formed by a supporter body portion having an air opening communicating with an air outlet/inlet of the carrier base, a flexible diaphragm and an outer ring. A wafer is uniformly pressed by the air pressure in the pressure chamber and fluctuation in the force pressing against the outer peripheral rim of the wafer caused by the wear of the retainer ring is countered by the diaphragm. Also presented in this document are embodiments in which holes are formed in the hard sheet and the soft backing sheet in the area of the wafer center by which it becomes possible to apply an additional back pressure for locally enhancing the polishing rate. These embodiments are, however, applicable only in case of specific known thickness variations of the semiconductor substrate and/or the polishing pad.
In U.S. Pat. No. 5,791,973 and U.S. Pat. No. 6,074,289 a substrate holding apparatus is described which contains a rotary shaft, a substrate holding head in the form of a disc which is provided integrally with the lower edge of the rotary shaft, a sealing member in the form of a ring which is made of an elastic material and fastened to the peripheral portion of the lower face of the substrate holding head, and a guiding member in the form of a ring which is fastened to the back face of the substrate holding head to be located outside the sealing member. A fluid under pressure, preferably air, is introduced into a fluid flow path formed in the rotary shaft from one end thereof and supplied to a space from the other end of the fluid flow path so as to form an air cushion on one side of the substrate and to press the substrate against the polishing pad. Due to the fact that the semiconductor substrate can be deformed in accordance with the surface of the polishing pad and/or the semiconductor substrate the semiconductor substrate can be pressed onto the polishing pad with a locally constant contact pressing force so that also the polishing rate is locally constant over the entire wafer. However, with this configuration it is not possible to introduce a specific local polishing profile by a local variation of the pressing force and hence the polishing rate.
The only way to achieve this would be the incorporation of a plurality of chambers to be supplied with fluids of varying pressure that appears too complicated.
In the introductory portion of U.S. Pat. No. 5,791,973 there is further described with respect to FIG. 16 another configuration of a semiconductor substrate holder wherein an elastic polishing pad is adhered to the top surface of a table. The bottom portion of a substrate holding head is formed with a recessed portion. The substrate is solidly supported by a plate-shaped elastic member that can be elastically deformed in the recessed portion of the substrate. The substrate holding head, elastic member and the substrate define a hermetically sealed space into which a gas under controlled pressure is introduced through a gas supply path. The gas under pressure introduced into the hermetically sealed space presses the substrate solidly supported by the elastic member against the polishing pad, so that the pressure on the upper face of the substrate achieves equal polishing. A disadvantage of the embodiment is the rather complicated mechanism of mounting and dismounting the substrate to the elastic member.
It is accordingly an object of the invention to provide a semiconductor substrate holder for chemical-mechanical polishing containing a movable plate which overcomes the above-mentioned disadvantages of the prior art devices of this general type, which allows polishing of a semiconductor surface with excellent uniformity over the entire surface area and which also allows the introduction of a specific wanted polishing profile.
With the foregoing and other objects in view there is provided, in accordance with the invention, a semiconductor substrate holder for holding a semiconductor substrate to be polished by chemical-mechanical polishing (CMP). The semiconductor substrate holder contains a main body for holding the semiconductor substrate in a predetermined position relative to the main body. The main body has a base plate and a ring-shaped elevation with an inner wall extending from the base plate. A pressurizing device is provided for pressurizing the semiconductor substrate from inside the ring-shaped elevation towards an underlying polishing pad. The pressurizing device has a movable plate disposed inside the ring-shaped elevation. The movable plate is mounted to the main body such that the movable plate is movable in a direction toward and away from the semiconductor substrate. A support member is disposed on a portion of the inner wall of the ring-shaped elevation. The support member has a support surface for supporting the semiconductor substrate.
With the semiconductor substrate holder according to the present invention the polishing operation can be performed in two basic operation modes corresponding to two different vertical positions of the movable plate.
In a first mode of operation the movable plate is in a lower position where it is in direct mechanical contact with the semiconductor substrate, preferably with a soft backing film in-between. The first mode of operation corresponds therefore to the standard carrier configuration. In the first mode of operation it is possible to vary the polishing profile in a predetermined manner, e.g. by applying a predetermined pressure to predetermined areas of the semiconductor substrate. This can be accomplished by a first fluid supply path formed through the movable plate and outlet openings formed in the lower surface of the movable plate and the backing film which outlet openings are connected with the first fluid supply path. Since the movable plate is in direct mechanical contact with the semiconductor substrate a pressure is exerted only on those substrate portions that are opposite the outlet openings of the movable plate when a fluid is supplied to the outlet openings.
In a second mode of operation the movable plate is in an upper position where it is not in direct mechanical contact with the semiconductor substrate. In this position a chamber is formed between the movable plate and the semiconductor substrate. By the first fluid supply path and the outlet openings formed in the movable plate a fluid, preferably air, can be supplied to the chamber so as to form an air cushion on one side of the substrate and to press the substrate against the polishing pad. This mode of operation allows a homogeneous pressurization of the movable plate and corresponds to the xe2x80x9ccushion modexe2x80x9d as known from the above-mentioned prior art documents.
In a preferential embodiment the first and second modes of operation are characterized by predetermined end positions of the movable plate wherein in a first end position corresponding to the first mode of operation a lower surface of the movable plate is in contact with the backside of the semiconductor substrate and in a second end position corresponding to the second mode of operation the lower surface of the movable plate is not in contact with the backside of the semiconductor substrate. The end positions of the movable plate can be defined by an abutment member that can be provided on an inner portion of the ring-shaped elevation. The abutment member may contain two abutment surfaces corresponding to the two end positions and the movable plate may contain an extension acting in combination with the abutment member.
On an inner portion of the ring-shaped elevation a support member is formed, which contains a support surface for supporting the semiconductor substrate. The support surface is flush with the surface of the movable plate in its first end position. In a preferred embodiment, the above-mentioned abutment member is formed integral with the support member.
In a preferential embodiment, the movable plate is actuated by applying a fluid pressure on one side thereof. The movable plate can be mounted on the main body by an impermeable sealing member like a membrane, so that a chamber is formed by the inner walls of the movable plate and the main body and the membrane. A second fluid supply path can be provided for supplying a fluid into the chamber for pressurizing the movable base plate and thereby effecting the movement of the movable base plate. Preferably the sealing member is provided with elastic properties like a spring such that a resting position of the spring corresponds to one of the first or second end positions of the movable plate.
In accordance with an added feature of the invention, the movable plate and the semiconductor substrate define a chamber, and a fluid supply path is fluidically connected to the chamber for supplying a fluid into the chamber. In a preferred embodiment, the fluid supply path runs through the movable plate. The movable plate has a further chamber formed therein and the further chamber is fluidically connected with the fluid supply path. The movable plate has a plurality of openings formed therein fluidically connecting the further chamber to the chamber.
In accordance with an additional feature of the invention, the movable plate has a main surface and the movable plate is movable between a first end position and a second end position. In the first end position, the main surface of the movable plate is in contact with a backside of the semiconductor substrate, and in the second end position, the main surface of the movable plate is not in contact with the backside of the semiconductor substrate.
In accordance with another feature of the invention, an abutment member is disposed on a portion of the inner wall of the ring-shaped elevation. The abutment member has two abutment surfaces corresponding to the first and second end positions. The movable plate has an extension acting in combination with the abutment member.
In accordance with a further feature of the invention, the fluid supply path is a first fluid supply path and a second fluid supply path is provided for supplying the fluid into a space between the movable plate and the base plate for pressurizing the movable plate and thereby effecting a movement of the movable plate.
In accordance with another added feature of the invention, a flexible connecting member connects the movable plate to the base plate. Preferably, the flexible connecting member is an impermeable sealing membrane, and the base plate, the movable plate and the impermeable sealing membrane define another chamber there-between.
In accordance with another further feature of the invention, the flexible connecting member is a spring member, and the spring member is connected to the movable plate and to the base plate such that in one of the first and second end positions of the movable plate the spring member is in a resting position.
In accordance with another additional feature of the invention, the support member is a part of the abutment member. Alternatively, the support member is directly connected with the abutment member or the support member is formed integral with the abutment member.
In accordance with a concomitant feature of the invention, at least one third fluid supply path is provided for supplying the fluid into an outer area of the chamber.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in a semiconductor substrate holder for chemical-mechanical polishing containing a movable plate, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.